Spontaneous and evoked excitatory junction potentials in rat tail arteries.

1. The frequency, amplitude and time course of spontaneous excitatory junction potentials (s.e.j.p.s) and their relationship to the time course and amplitude of evoked excitatory junction potentials (e.j.p.s) were examined. 2. The frequency and amplitude of s.e.j.p.s varied dramatically between cells. There was good correlation between their rise and decay times. 3. The amplitude and time course of e.j.p.s also varied between cells. E.j.p.s with large amplitudes and fast time courses were recorded in cells with high s.e.j.p. frequencies. 4. Active responses propagated only for very limited distances. 5. The frequency of s.e.j.p.s decreased after reserpine and 6-hydroxydopamine (6-OHDA) treatments, suggesting that s.e.j.p.s were related to spontaneous release of noradrenaline from nerve terminals.